1. Field of the Invention
The present invention relates to mixed bed deionizing units and, more particularly, to means for controlling the in situ regeneration of the mixed bed resins.
2. Prior Art
For the purposes of this invention, mixed bed deionizers can be generally grouped into two types, those which have their resins removed for recharging and those which have their resins regenerated within the deionizer tank. The present invention relates to the latter type in which a system of valves, drain pipes and regenerating fluid distribution conduits are necessary for regenerating the resins in situ.
In this type of device, during service the cation and anion resins are relatively uniformly mixed throughout the deionizer tank. To regenerate the resins they are initially backwashed to remove the turbitity and separate the cation and anion resins due to their size and density differences. It is also common to use an intermediate inert resin of lesser quantity than the anion and cation resins and which, upon backwash, settles out to a position intermediate the anion and cation resins to act as a buffer zone during regeneration.
In such devices, the resins settle in the tank after backwash with first the anion resin, then the inert resin, and finally the cation resin, going from the top to the bottom of the tank. The inert resin settles out in the tank at a position where an intermediate collector extends into the tank for withdrawing the anion and cation regeneration fluids which are respectively introduced from the top and bottom of the tank and flow through the anion and cation levels to the inert intermediate level and are withdrawn through the collector system and passed to drain.
All of these mixed bed deionizers which regenerate in situ utilize an extremely complex and expensive external piping and valve arrangement in order to introduce and withdraw the regeneration chemicals and backwash and rinse liquids at the proper locations in the bed and in an appropriately timed sequence. The initial set-up expenses of such devices are a major portion of their cost because of the labor required to put together all of the pipes, valves and electrical control equipment for each installation. In addition, there are a large number of valves associated with each mixed bed deionizer which also is a substantial portion of the cost of an installation.
A major problem associated with such prior art mixed bed deionizers and their control systems lies in the inability to determine the exact location in this complex networks of piping and valves where a malfunction occurs. It sometimes becomes necessary to dismantle almost the entire system and check each component to locate the fault.